Conventionally, devices using a transparent conductive film have been developed. Examples of such devices include liquid crystal display devices, solar cells, organic EL devices, optical devices such as inorganic light-emitting diodes (inorganic LED), and coordinate panels referred to as touch panels. Indium-tin oxide (ITO) films are generally used as transparent electrodes or transparent wiring in these devices. The transparent wiring usually has a very long total length and therefore requires flexibility. ITO is, however generally brittle and apt to be cracked by bending or other stress. Cracking of the ITO film leads to an increase in electrical resistance.
The use of carbon materials (a carbon fiber, a carbon nanotube, graphene, or the like) as a conductive material can significantly reduce the amount of rare metals or the like to be used. In some cases, the use of carbon materials even enables no metals or the like to be used. Carbon materials have high flexibility and large mechanical strength, and in addition, are chemically stable. Although individual molecules of carbon materials have comparatively high conductivities, the resistance in intermolecular conduction is high. For this reason, when carbon materials are used as a transparent electrode having a large area, the electrical resistance is higher compared to an ITO film of the same light transmittance. When carbon materials are used for wiring with a long total length, the electrical resistance is much higher than that when a metal conductive material such as copper (Cu) is used.
Since a metal nanomaterial has high conductivity, development for improving the conductivity of carbon materials by using a composite of the carbon materials and metal nanomaterial is underway. However, even when the composite is used, it is difficult to obtain a transparent conductor which has high transparency, is excellent in resistance to bending, peeling, and impurities, and is obtainable at low cost.